The present invention relates to a one or two dimensional lens support structure for use with laser diode arrays. More particularly, the invention relates to a structure for mounting one or a plurality of lenses on a substrate as a subassembly of working lenses, and to a method of fabrication of such a subassembly. The invention has application in many areas requiring collimation, focusing, or other direction of light emitted by high power semiconductor lasers, including satellite communication directed energy applications, range finding, isotopic separation, pumping of solid state laser systems, and fiberoptic coupling.
Laser diodes are semiconductor structures capable of converting electrical power into optical power with very high efficiency (typically 50%). The present inventor has received patents which disclose and claim laser diode arrays, including U.S. Pat. Nos. 5,040,187, 5,128,951, 5,264,790 and 5,311,535. The disclosures of these patents are incorporated herein by reference.
In recent years, there have been substantial improvements in the quality and availability of GaAs base laser diode material. In addition, it has become possible for a laser device producer to customize the output wavelength of the emission of laser diodes. The ability to grow laser material for emission at wavelengths of 630 nm to 2 microns means that laser diodes have become a preferred device for fabrication of narrow wavelength emission devices. Many of these devices are of relatively low power, such as those used in laser printers and CD devices, which have power levels on the order of a few milliwatts. However, when individual devices are grouped together, with proper heatsinking, tremendous peak and average power levels can be generated. It is not unusual for several thousand emitters to be packaged into just one square centimeter (1 cm.sup.2), the package having an optical emission of several thousand watts of peak power and average powers of from 1 to 100 watts per square centimeter. (Powers are expected to climb even higher in the near future.) These higher power laser diode arrays can be used in simple high power flashlamps for night vision systems, or in very high speed, high intensity flashlamps used in very high speed photography.
Two of the major applications for large very high powered laser diode arrays are for pumping of solid state lasers, such as YAG laser systems and fiberoptic bundles. The outputs from the diode pumped solid state lasers are used in many diverse applications, from so-called target designators, to simple cutting operations, to various types of laser based surgery. Direct diode pumping of fiberoptic bundles typically is used for medical devices, and/or where space requirements do not allow for locating actual laser diode arrays at the point at which the emissions are needed. That is, there may be space for a fiberoptic bundle, but not for the diode array module and associated support equipment.
Diode lasers themselves present problems, with respect to emission area and emission characteristics. During the growth and fabrication of the laser diode device itself, the actual device emission area is extremely small (on the order of 200 microns.times.1 micron). (By comparison, the typical human hair has a diameter of 100 microns.) Light emitted from such a source does not come out of the device in a narrow "beam," such as that normally seen in laser photos and demonstrations, but instead fans out very quickly. Typically, the divergence of this light can be from 60.degree.-90.degree. (typically 60.degree. ) in one axis, (known in the industry as the fast axis because of its relatively fast divergence), and 10.degree.-30.degree. (typically 10.degree.) in the other axis, (known in the industry as the slow axis because of its relatively slow divergence). Examples of the divergence of the light in the different axes is shown in FIG. 1, relative to a typical laser diode bar 1.
While the emission's light intensity and tight wavelength still make laser diodes useful, if the light could be collimated, that is, made to travel in a column or a straight line, laser diodes would become still more useful. They also would become more useful if the light could be not only collimated, but also focused, that is, made to travel toward a desired focal point. It also would be useful to limit the "fanning out" of the light by limiting its divergence along the fast axis.
Single laser diode devices, which typically are used in laser printers, CDs and fiberoptics, now provide collimated emissions by using various lens arrangements in front of the laser diode. This technology is well developed and described throughout various technical journals. With ever increasing interest in very high power laser diode arrays, capable of producing multi-kilowatt peak powers, much work has been done trying to mate optics with laser diode arrays in order to provide collimated emissions. While the best answer would be to mold a lens, with the proper dimensions and curvatures, to collimate the emission, it has been difficult to produce such an optical device. While it is possible that a molded lens will be made successfully in the future, for the present individual optics appear to provide the most ready answer to collimation of emissions of laser diode arrays.
Collimation or focusing of laser diode emissions via the use of optical elements requires a very high level of mechanical precision. Not only do the optical elements need to be made to the correct dimensions, but also each of the individual lens elements then need to be located precisely with respect to the others, and more importantly to the emission area for the laser device itself. An example of the necessary accurate positioning is seen in FIG. 2, in which a laser diode bar 1 is shown with a collimating lens 2.
What is necessary to implement the FIG. 2 positioning is an appropriate lens support structure. Such a structure also could be used to enable focusing of light from laser diodes, or alternatively to limit the amount of divergence of light emitted from laser diodes.